1. Field of the Invention
This invention relates to a composition of matter particularly useful in dishwashing compositions for hard-surfaced materials and to the dishwashing compositions themselves, which are particularly useful for washing crockery at low temperatures with minimal foaming. Substances and stains that are normally difficult to remove, such as those containing solid fat, are removed by compositions of the present invention at low washing temperatures.
2. Description of the Relevant Art
Alkaline detergent compositions used in the past for the machine washing of crockery have consisted essentially of inorganic salts, such as alkali phosphates, alkali silicates and alkali carbonates, active chlorine donors and, to improve their wetting power, have contained small amounts of a low-foaming nonionic surfactant. The compositions can show high cleansing power with respect to food remains of all kinds at normal working temperatures of from 55.degree. to 65.degree. C.
Improved, enzyme-containing dishwashing preparations of the type described in German Offenlegungsschrift 17 67 567, have been developed with a view to preventing the formation of thin films which can gradually build up on the surface of the crockery. These thin films, which usually consist essentially of starch and, possibly, traces of protein, may spoil the appearance of the washed crockery.
To save energy, many manufacturers have marketed energy-saving dishwashing machines which are not only reduce the water consumption of the wash liquor from 10 to about 6-7 liters, but also offer an economy program using a greatly reduced temperature. For example, the "Favorit de Luxe Elektronik i" domestic dishwashing machine marketed by AEG needs only about 6 liters of water for the wash liquor. The power consumption of the "40.degree. C. normal" program (clear rinse temperature: 55.degree. C.) amounts to only 1.1 kW/h as compared with the conventional consumption of 1.9 to 2.2 kW/h at 65.degree. C. Practical experience with this machine, however, has shown that the change from the 65.degree. C. program to the 40.degree. C. program can reduce the cleansing power of the normal 30 g of standard dishwashing composition (approximately 5 g/l) by an average of 1.4 points in the case of 8 test residues.
To improve the performance of dishwashing compositions at the lower wash temperatures used by energy saving machines, a number of additives have been tested. For instance, the addition of 1% of an amylase-protease mixture in the wash cycle can improve the removal of oatflake and starch residues. Addition of lipase to the composition to increase the removal of fats seems to have had little effects. Despite the use of these additives, it has been difficult to remove food remains containing solid fat at temperatures around 40.degree. C.